How to Apply Varnish
The preparation for a varnish finish should be more thorough than those needed for an opaque painted finish since the transparent varnish would show up each flaw in the wood. Be sure to sand the surface as smooth as possible and take away all stains or blemishes prior to starting. Then dust really well. The fine grit left after sanding is a basic cause of rough-looking, "sandy" finishes.
A fine quality bristle brush, utterly clean, is a big must for great varnishing. The brush must be soft and pliable having plenty of flagged bristles. Don't dip it into the varnish more than one-third its total length, and always flow the varnish on liberally using long strokes put on parallel to the grain. Most important of all, don't wipe excess varnish off the brush by dragging the bristles around the rim of the can. Alternatively, tap the tips of the bristles lightly on the inside of the container just above the surface of the liquid. Wiping across the rim creates tiny bubbles to build up in the fluid and these would make it almost impossible to achieve a smooth finish.
Air bubbles on the surface could also be caused by pressing down too hard on the brush. Varnish must be brushed on using only light to medium pressure. After covering the panel in one direction, cross-stroke right away by brushing across the grain at right angles to the first strokes. Finish off by gently stroking a third time along the grain, with an almost dry brush and touching the surface with only the tips. This crisscrossing method will virtually eliminate all brush strokes so that a consistent application is guaranteed.
Varnishing must never be performed in a dusty location, or in garages or basements that are damp or cold. If possible, lay the pieces horizontally, and always take out all hardware and knobs prior to starting. Chests or cabinets that have drawers should be done with the drawers removed so that each one can be placed in a horizontal position with their faces up.
If more than one coat of varnish will be applied, the first coat must be thinned using 10 per cent turpentine. Successive coats can then be put on as they come from the can. For a super-smooth finish, sand lightly between coats. Use #2/0 very fine sandpaper and rub along the grain. Remember to dust completely before applying the next coat. The best way to gel all the dust is by using a tack rag, a sticky cloth which you can get in many paint and hardware stores.
The right kind of varnish is just as important as the techniques involved. As opposed to popular opinion, varnishes are not alike and all are not suited for every job. Most well-stocked paint stores have many different types, each made for one or more specific purposes. To be sure you are getting the correct one for the job, read the label carefully.
Varnishes vary in many aspects. Some are clearer than others —a crucial point to take into account when light finishes are involved. Varnishes also vary in their impedance to water and alcohol staining and in the degree of gloss of the final finish. Some dry having a super high gloss, while others dry to an entirely flat finish. For most furniture and paneling, a semi-gloss or satin-finish varnish is preferable. This gets rid of the need for rubbing down or dulling the final coat.
As a general rule, the glossy varnishes have a tougher finish than dull ones. For this reason professionals would like to use hard-drying, glossy varnishes on counter tops, table tops and other surfaces which get hard wear. They allow the final coat to harden completely, then rub it down to a smooth, satin finish which, while still being lustrous, doesn't have an unpleasant "wet" shine.
For this kind of rubbed finish a special varnish is generally used. Known as a cabinet rubbing varnish, it dries in one day to an exceptionally hard finish which takes on rubbing beautifully. The handyman concerned in trying his hand at this type of finishing operation would need some powdered pumice stone, powdered rottenstone and crude oil.
Let dry the final varnish coat till completely hardened (check the label), then make a paste of the pumice stone and crude oil. Mix the two together right on the surface, then fold a heavy, lint-free cloth into a small pad. Press this pad into the paste and rub over the surface using straight strokes along the grain. Use only a medium pressure and rub until the surface feels smooth and is free of all blemishes.
Use a clean, dry cloth to wipe all pumice off the surface. Use a different cloth moistened with turpentine to clean away the residue then wipe again with a clean cloth till the surface is dry. This would leave the surface a bit cloudy because of fine scratches which are created by the pumice stone.
To restore the luster, a second rubbing is needed, this time using powdered rottenstone and crude oil. Mix a paste just like before then rub using a pad of clean felt or similar material. Rub in straight strokes along the grain. When the surface has been polished to the luster desired, wipe away all the paste using a clean cloth and polish with a soft dry cloth till the surface is very clean and dry that the polishing cloth creates a squeaking noise under your hand. A good quality furniture polish can then be put on after a day or two.